The Root Route

Why don’t roots push a plant right out of the ground?  It’s a question only a scientist or an 8-year-old kid would ask.  The answer is more amazing than either would have realized.  Root hairs feel their way around obstacles and find the openings, in the dark, by means of a complex interplay of proteins and signaling molecules.  The story is told in Science Daily.
    Production of a protein called RHD2 at the tips of root hairs is controlled by a self-reinforcing cycle.  Obstacles break the cycle and allow growth in another direction.  “This remarkable system gives plants the flexibility to explore a complex environment and to colonise even the most unpromising soils,” said Professor Liam Dolan at the John Innes Centre in Norwich.  “It also explains how seedlings are able to grow so quickly once they have established.”

From the humblest weed to the most magnificent tree, plants are improbable wonders.  Their roots can conquer soils hard as rock and their stems can crack granite.  Roots pump nutrients and water from deep underground to the top needles of a redwood nearly 350 feet in the sky.  How can such things be?  We are only beginning to understand.
    To view a plant at the macroscopic level is to miss most of its wondrous operations.  Adolescent students do science projects with bean seeds.  They watch the roots go down and the stems go up.  It seems perfectly natural.  Why should it look natural?  Rocks and pebbles and other lifeless things don’t typically push against gravity or grow downward through a junkyard of obstacles.  Life goes against the natural grain of the laws of physics (e.g., gravity) only by capturing energy and harnessing it with programmed controls that build and operate molecular machines and perfectly-adapted building materials.
    Students observe root hairs through their cheap microscopes.  They seem like nothing particularly special or interesting.  Adding the temporal dimension with time-lapse cameras creates a little more interest.  But without modern biology’s improved techniques for observing things at the microscopic and nanoscopic levels, who would have imagined what really goes on in those tiny root hairs?  There is more designed complexity in the weed growing through a sidewalk crack than in the textbook that catalogs it.  Try not to feel guilty when pulling, poisoning or hacking the weeds in your garden today.